Copolyesters derive this combination of properties from the molecular structure of the linear chains composed of hard segments having crystalline properties and soft segments having elastic properties. For a good serviceability, the hard segments should have a melting point which is at least higher than 100.degree.C., preferably higher than 150.degree. C. and still more preferably higher than 175.degree. C. To retain elastic properties at lower temperatures, the soft segments have a glass transition temperature of less than 20.degree. C., preferably less than 0.degree. C. and still more preferably less than -20.degree. C.
In the conventional thermoplastic copolyester elastomers according to the prior art, which has been extensively described, inter alia, in Encyclopedia of Polymer Science and Engineering, Vol. 12, page 75 ff. (1988) and the references listed therein, the hard segments are generally made up of units derived from an aromatic dicarboxylic acid and an aliphatic diol and the soft segments of polyester units derived from aliphatic dicarboxylic acids and aliphatic diols or from lactones or soft segments composed of aliphatic polyether units.
The conventional thermoplastic copolyester elastomers having good mechanical properties and easy processability have, however, some specific disadvantages. Thus, the copolyesters having soft polyether segments are not so good as regards thermal stability and the copolyesterester elastomers are susceptible to hydrolysis.
The subject of the invention is a copolyester elastomer which has both superior thermal oxidative stability and stability towards hydrolysis.